1. GPS SKY What is the Sky Doing Today?

2. Objective

3. Summary of Topics - Importance of Planning - Review how GPS Calculates Positions - Check Out The Sky - Planning Ahead

4. Planning the GPS Day Recreational GPS is very forgiving It’s for fun! Not for worrying about PDOP,SNR,Mask Angle,blah blah… Designed to Work inside your Pocket! Still important - as will be demonstrated

5. Tracking a GPS Satellite Vehicle (SV) One of 29 12,000 miles up 6000 mph JTRACK http://liftoff.msfc.nasa.gov /RealTime/JTrack/3D/JTrack3D.html

6. How to Calculate a Position Measure the Distance to the Satellites

7. How to Calculate Distance Speed of Light x Travel Time Distance Time signal left satellite Current time

8. Minimum # of Satellites Required 4 Unknowns Require 4 Satellites time...………………(1)satellite latitude …………….(1) satellite longitude.………….(1) satellite elevation …..…….…(1) satellite 4 Satellites = 3D Good 3 Satellites = 2D BAD A Garmin will allow 2D positioning! Watch Out!

9. -Want tetrahedron as large as possible -Want index as low as possible PDOP Position Dilution of Precision

10. Garmins View of Mapping Typical Mapping Grade GPS Settings - PDOP = 99 - SNR = 2 º - Mask Angle = 5 º PDOP = 6 SNR = 6 Mask Angle = 15º

11. Rules of Thumb PDOP of 6 or Less - Good DOP of 3 or Less - Good PDOP / DOP Position Dilution of Precision Garmin only Shows DOP That’s 1/2 of PDOP

12. Tools for Predicting - See PDF on How To: CD</software/TrimblePlanSoftware : Almanac File: Software: From CD </software/TrimblePlanSoftware or http://www.trimble.com/planningsoftware_ts.asp

13. PDOP and Visibility Graphs Instructor Runs Trimble Planning Software for Today Instructor Runs Trimble Planning Software for Today

14. PDOP and Visibility Graphs

15. It’s Your Decision Plenty of satellites In a hurry to go Limited control Must collect now Reasons to plan Reasons not to plan More efficient More economical Forewarned

16. Plan Ahead External Antenna Wait till Good Sky Returns Offsets Map Using other Means? Steps You Can Take

17. 17 Coming Up –GPS Sky –Garmin SetupGarmin Setup –Get Outside! Break